(Mg0.5Zr0.5)xAl1−xN and (Mg0.5Hf0.5)xAl1−xN thin films are AlN-base piezoelectric materials, and their piezoelectric coefficients are higher than those of pure AlN, being promising materials for acoustic devices. However, their acoustic properties remain unknown because of measurement difficulty for deposited thin films. In this study, we measure their longitudinal-wave elastic constants C33 and their temperature coefficients using picosecond ultrasound spectroscopy for 0 < x < 0.13; we obtain C33 = 398.2 ± 0.7 GPa for pure AlN, and it largely decreases by doping Mg, Zr, and Hf, leading to a minimum values of 316.8 ± 1.6 GPa for (Mg0.5Zr0.5)0.126Al0.874N.
We measured the temperature dependence of the elastic constant C11 of a 12C diamond monocrystal using picosecond ultrasonics between 10 and 613 K. We found that C11 is almost temperature independent below room temperature; the temperature coefficient around 300 K is −6.6 MPa/K. Our results show a significantly higher Einstein temperature than reported values by ∼30%, indicating that diamond has a larger zero-point energy, which remains dominant around ambient temperature. We also calculated the temperature dependence of the elastic constants using ab-initio methods, resulting in good agreement with measurements. Our study shows that below-ambient-temperature measurements are not sufficient to extract the Debye temperature and the Grüneisen parameter of high-Debye-temperature materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.